2,7-Naphthalenedisulfonic acid, 4-amino-3,6-bis[2-[4-(ethenylsulfonyl)phenyl]diazenyl]-5-hydroxy-, sodium salt (1:2)

Endpoint summary

Additional information

The test substance, Reactive Black 5 bis-vinyl, is a solid under all environmental conditions and is highly soluble in water. It is expected to have a low volatility based the melting point and vapour pressure and it is expected to have a low affinity for soil/sediment based on the low Log Kow value. As such, any environmental release will result in virtually all of the substance compartmentalising into water compartments, with little release directly to atmosphere or compartmentalising to soil/sediment compartments.

Any potential exposure to the environment is predicted to result in rapid redistribution to water; due to its low volatility, high water solubility and partitioning values it is indicated that the majority of the substance would eventually partition to water rather than to soil and sediment should it be released to the environment.

A Level III fugacity model was conducted in the US EPA EPISUITE (Mackay et al., 1996a, 1996b; Mackay 1991) which assumes steady-state but not equilibrium conditions. The Level III model in EPI Suite predicts partitioning between air, soil, sediment and water using a combination of default parameters and various input parameters. This model has been used to calculate the theoretical distribution of the substance between four environmental compartments (air, water, soil, sediment) at steady state in a unit world. This modelling indicated a distribution to firstly soil and secondly sediment. It is proposed that although the majority of the substance distributes to the soil/sediment compartments within the model, the high solubility in water indicates that the substance is more likely to distribute to water – e. g. soil pore water.

This assumption is confirmed by the model for the STP Overall Chemical Mass Balance in the US EPA EPI SUITE, which shows that 98% of the influent of the dye is in the water phase.

Reactive Black 5 bis-vinyl displayed low biodegradability, which indicates that it is unlikely to achieve a half-life of less than 40 or 60 days within fresh water or marine water, respectively, attributed to ready biodegradation alone.However, it is rapidly hydrolysed with a half-life of 1 to 2 days at pH 7. When Reactive Black 5 was applied to sediment/water at a final concentration of 1 mg/kg in the test system, the test substance was rapidly degraded. The DT50 of Reactive Black 5 was 2 days. After 3 to 6 days, only 10% of the applied Reactive Black 5 could be found. All metabolites decreased at the end of the test period to levels around the lower level of quantification. Consequently, an accumulation of metabolites could be excluded. The majority of the metabolites of Reactive Black 5 were deposited in form of non-extractable residues in sediment during test phase. After about 1 month, mineralization of the metabolites started.

Studies on direct phototransformation in water are not available but it was found that the sulfonated azo dyes can be destroyed by UV photooxidation process (Saliha et al. (2005)). The kinetics of the degradation depends on the azo, benzene and naphthalene groups of the dyes. The first step of the degradation is related to cleavage of the azo bond of the molecule and naphthalene ring, which leads to further degradation until complete mineralization.

It is therefore concluded that abiotic processes would contribute significantly to the depletion of the substance within the environment.

Reactive Black 5 bis-vinyl has a low log Kow, which indicates that possible bioaccumulation in the food chain is not anticipated. A bioaccumulation study on Reactive Black 5 in the carp revealed bioconcentration factors < 11 for 0.2 mg/L and < 1.1 for 2 mg/L. Hence, Reactive Black 5 either as bis-ester or as bis-vinyl does not bioaccumulate in the aquatic compartment. Based on data from kinetic and metabolism studies in rats (oral and intravenous administration), Reactive Black 5 does not have any bioaccumulation potential in animals.

Adsorption to soil is deemed to be low, based on the low adsorption and partition coefficient values and high water solubility. Such a low potential indicates that the substance is unlikely to bind tightly to soils and sediments and instead partition almost exclusively to water. As such, significant exposure related effects to sediment and soil dwelling organisms are considered to be negligible.

Based on its high water solubility, low partition coefficient and fairly rapid hydrolysis rate at environmentally relevant pHs, it can be concluded that it is unlikely that Reactive Black 5 bis-vinyl could potentially be persistent within the environment. Abiotic effects within the environment will result in eventual removal from the environment and hence significant contact with the organisms in the food chain can considered to be minimised.

Finally, Reactive Black 5 bis-vinyl demonstrates low acute toxicity in mammalian studies therefore in the event of exposure to environmental organisms, effects due to secondary poisoning can be excluded.